Continuous strip-annealing furnace



March 31, 19420 A. N. OTIS ETAL CONTINUOUS 'STRIP-ANNEALING FURNACE Filed Nov. 2'7, 1940 2 Sheets-Sheet l Inventor-s: Albert N. Otis, Franci5 Mohler',

Their Attorney.

March 3i, 1942. A. N. OTIS ETAL 2,278,136

CONTINUOUS STRIP-ANNEALING FURNACE Filed Nov. 27, 1940 2 Sheets-Sheet 2 Inventors:

Albert N. Otis, Francis Mahler",

T, heir Abbot-neg.

, in order to produce the tonnage required.

may, for example, have a height of about 75 feet Patented Mar; 31, 1942 UNITED STATES: PATENT OFFICE CONTINUOUS STRIP-ANNEALENG FURNACE Albert N. Otis and Francis Mohler, Schenectady, N. Y., assignors to General Electric Company, a corporation of New York Application November 27, 1940, Serial No. 367,398

, Claims.

invention is a further development of-the fur-- nace disclosed and claimed in the Otis Patent 2,181,738, November 28, 1939.

A furnace of the character disclosed in that patent must necessarily be of large physical size It and a width sufficient to pass two 36 inch strips which, traveling at a speed of say 70 feet per minute, would amount to an output of approximately 10,000 lbs. of material per hour. With a furnace of this size producin material on a large tonnage basis, it is obviously important that the continuity of service be maintained and it is exceedingly important that the strip should not be broken in the furnace since that would result in a serious delay in the annealing process. furnace such as disclosed by the aforesaid patent, if considerably increased in height, it is possible that a strip might be broken in the furnace by application of tension on the high temperature or down-travel side with the attendant delay until the strip is rethreaded, and should both strips be broken at the same time a shut down of approximately two days might be required to enable the furnace to cool down sufiiciently to permit the rethreading of the two strips therethrough and the resumption of operations. For these reasons it will be seen that it is imperative to construct the equipment in such a manner that as long as the prescribed operating procedure is followed a strip will never be broken in the furnace. Such a construction therefore is the object of our invention.

With a driving mechanism for the strip, such In a siderable amount above that due merely to the weight thereof. Moreover it would be possible for an operator inadvertently to readjust the control of thelatter motor in such a manner that the highly heated part of the strip in the furnace would be stressed beyond its breaking point. In a furnace of this character where the strip hangs freely in a long-length in the heating chamber the stress in the strip due to its own weight cannot of course be avoided but in accordance with our invention it can be safeguarded against being I subjected to any material additional stress. This as that disclosed in the aforesaid patent, where the strip is driven at the top of the furnace by one motor and is drawn through the cooling chamber by another motor having a separatespeed control forkeeping taut the strip in the cooling chamber, variations in elongation of the strip, due to changes in its temperature, as it proceeds through the chambers of the furnace, or variations in the traction of the trip on, the rolls of the horizontal cooling chamber, might affect the stresses imposed upon it and under certain conditions might be enough to raise the stress. in the strip at the top of the hot chamber l2 9. conwe accomplish by causing the strip to pass through a depending loop at the lower end of the freely hanging part and by automatically regulating the speed at which the strip is drawn through the cooling chamber in accordance with the depth of the loop. v

Our invention will be better understood from the following description taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.

Referring to the drawings, Fig. 1 is a side view partly in section of one embodiment of our invention; Fig. 2 is a combined vertical cross sectional view drawn to a larger scale and circuit diagram thereof, and Fig. 3 is a similar view taken at right angles to that of Fig. 2. In the drawings, l is the outer steel shell of the furnace which is supported in an elevated position by the base structure 2. The top of the shell I is covered by the cap 3 to facilitate accessibility to the strip supporting roll. Within the shell and the cover isthe layer 4 of heat insulating material which has the lining 5 of a suitable refractory material. Extending across the upper portion of the furnace is the partition I forming the upper chamber 8 in which is housed the strip supporting roll. Beneath the partition I is the vertical partition 9 and the horizontal partition l0 which partitions form the two heating chambers I l and 12, on the walls of which are mounted electric heating units 1 3, the preheating chamber l4 and the cooling chamber I5. By way of example, the chamber II for a certain character of steel strip annealing may be kept at a temperature of 1300 F. and the temperature in the other chamber i2 may be kept at 1800 F., it being understood that the strip progresses through chambers 14, ll, I2 and IS in the order mentioned. A protective atmosphere which may circulate through the chambers may be admitted to the furnace by the pipe l6.

Arranged in the upper chamber 8 is the single long roll or drum it which serves to support the two separate strips i! of the material being anhealed; in the furnace. Since each strip must conform to the curvature of the roll by which it is supported the diameter of the roll or at least that part of it which contacts with the strips is relatively large. The roll at each end has a tapering portion which terminates in a shaft which extends through the furnace wall and forms a journal which engages one of the bearings 20. These bearings are mounted on the brackets 2|, suitable stumng boxes 22 being provided where the shafts pass through the outer shell 4 of the furnace. For driving the roll we employ the motor 22 mounted on one of the bracket 2!, the motor being connected to the shaft of the roll by suitable worm gearing. Each of the two strips being annealed in the furnace is suspended from the roll II, the strips passing through suitable openings 26 in the partition I and also through similar openings 26 in the bottom of the furnace.

Within the base portion 2 of the furnace, which portion constitutes a second cooling chamber, are two pairs. of cantilever rolls 28 and 29 which are supported by. the bearings 30. The rolls 28 serve to guide the strips as they enter the chamber I4; the rolls 29 arearranged normally to be out of contact with the strips as they pass through the base but are arranged to be engaged by the strips in the event that by accident they shouldbe withdrawn from the base faster than they are being fed along by the upper roll ll. We have shown the rolls 20 as idlers but in certain cases -we may prefer to drive them. By means of the pinch rolls 32 driven by the motor 32, which is connected with the source 34, each strip is drawn from the previous apparatus or from a reel and the entrance to the furnace. To insure a uniform and light tension in the strip at all times as it is fed to the furnace the strip passes from the pinch rolls into the loop 35 and the speed of the motor 33 is controlled by the depth of the loop.

For effecting this control we have shown the rheostat 26 in the motor circuit provided with an arm having the idler 31 engaging the loop. The moving parts of this control apparatus preferably is made as light as practicable to avoid unnecessary tension in the strip entering the furnace. and so that it will be readily responsive to changes in tension.

As the strips emerge from the base of the furnace they pass through the third or main cooling chamber 40. In this chamber each of the strips is supported on a series of driven rolls, one set being designated 4|, and the other set being adjacent, which rolls 4| are shown as being driven from the common shaft 42 through the spiral gears 43. The shaft 42 is driven from the motor 44 through the worm gearing 45. It is understood that two such drives are employed, only one of which is shown. The strips are withdrawn from the cooling chamber by any suitable means such, for example, as the motor driven pinch rolls 41. To insure a uniform and light tension in the strips at all times as they are withdrawn from the cooling chamber we cause the strips to pass through the loops 48 before they reach the pinch rolls, and regulate the speed of the motor 49 which drives the pinch rolls in accordance with the depth of that loop. The means shown for effecting this control'is like that for controlling the motor 33 and includes the rheostat 50 whose arm has the idler i engaging the fed to the roll 28, a suitable seal being provided at I loop in the strip. The moving parts of this control apparatus preferably also are made light to avoid unnecessary tension in the strip. Beyond this the strip is shown being wound on the reel 62 which is driven by the motor 52 whose speed is regulated by a loop controlled rheostat.

With an arrangement such as shown in the aforementioned Patent 2,181,738, it will be seen that the strip in the hot chamber 12, where it is the weakest, is subjected to a tension due to the combined eifect of the weight of the suspended part thereof and any pull of the rolls 4| and the pinch rolls 41 over and above what is required to overcome friction. There is always the possibility, particularly in the case of a very tall furnace, that an operator will inadvertently readjust the control circuit of the motor driving the pinch rolls or the motor driving the rolls 4i or both in a manner which will impose an excessive pull on the strip or will give the strip a jerk which added to the tension due to its weight may cause the strip to part. For example, with a cooling chamber 125 feet long provided with such driven rolls as would be required and ignoring the pull of the pinch rolls, the traction of the rolls on the strip would be approximately the weight of the strip times the coeillcient of friction of .2. This would be equivalent to approximately 25 pounds and with a strip having a cross sectional area of 0.3 square inch the tension in the strip due to the rolls I would be approximately pounds per square inch. This added to the tension in the strip due to its weight in the chambers l2 and il would give an approximate tension of 300 pounds per square inch.

In accordance with our invention we avoid the possibility of subjecting the hot strip to any material tension above that due to its own weight. that is, the weight of the suspended portion of the strip. This we accomplish by causing the strip at the lower end of the hot suspended part to terminate in the loop 54 from which the strip passes on into the cooling chamber 40. Between the loop and the cooling chamber we have shown the strip supported by other rolls 55 which may or may not be driven. We employ means for automatically maintaining the depth of the loop 54 within definite limits whereby the traction of the driven rollsin the chamber 40 cannot increase the tension in the strip above that due to the weight of the suspended portion or transmit a jerk thereto.

The means which we employ for maintaining the depth of the loop 54 approximately constant is substantially the same as that disclosed in the Otis Patent 2,060,634. As in that patent, two light beams are employed which are arranged to be engaged by the two photoelectric devices 55 which, through the amplifying means 64 and 61, operate the relays, 65 and 69. These relays control the switches 68 and 59 which, through the resistors 58 and 60, control the speed of the motor 44. The operation of the switches 65 and $9 in response to the interception of the light beams by the loop in the strip also operate the switch 15 to control the operation of the motor 12 which by changing the setting of the rheostat 5i makes a slight change in the speed of the motor 44. Inasmuch as the control mechanism of the motor 44 is not a part of the present invention but is employed merely to maintain the depth of the stant depth of the catenary a more detailed description of the control apparatus and its operit passes toward the heating chambers, through the cooling chamber and finally to a reel as well as the speed control means employed are in duplicate, whereby each strip is supported and moved independently of the other with the exceptionthat the single roll l8 at the top of the furnace supports and drives both strips. motor 23 which drives the roll l8 and whose circuit connections are not shown in the drawings may be of any well known construction wherein the speed can be adjusted for the desired range of travel speeds of the strips through the furnace. It would be supplied from the same power source and its control means would be coordinated with that for the other motors shown;

What we claim as new and desire to secure by Letters Patent of the United States, is:

1. A continuous strip-annealing furnace having a vertical heating chamber and a horizontal cooling chamber connecting therewith, a driven roll for suspending a part of said strip vertically in said heating chamber, means for drawing said strip through said cooling chamber from said heating chamber, and means for preventing the The vertical part of the strip from being tensioned by said drawing means an amount greater than that substantially equal to its weight, said latter means comprising apparatus for regulating the speed of said strip drawing means and a photoelectric device for controlling said regulating apparatus in accordance with the depth of a free depending loop in said strip between the vertical and the horizontal parts thereof.

2. A continuous strip-annealing furnace having a vertical heating chamber and a horizontal cooling chamber connecting therewith, a roll from which a part of said strip is suspended vertically in said heating chamber, means for driving said roll at a. uniform speed to feed the strip into the suspended part, rolls in said cooling chamber for supporting the strip therein after it leaves the heating chamber, a motor for driving said rolls and means for preventing said drawing means from causing a tension in said strip at the upper end ,of said vertically suspended part thereof substantially greater than that equal to the weight of said vertically suspended part comprising a photoelectric device arranged to control the speed of said motor in accordance with the depth of a free depending loop in the strip between the vertical part and the horizontal part of the strip.

ALBERT N. OTIS. FRANCIS MOHIER. 

